A Gate‐Tunable Ambipolar Quantum Phase Transition in a Topological Excitonic Insulator
Yande Que, Yang‐Hao Chan, Junxiang Jia, Anirban Das, Zhengjue Tong, Yu‐Tzu Chang, Zhenhao Cui, Amit Kumar, Gagandeep Singh, Shantanu Mukherjee, Hsin Lin, Bent Weber
Abstract
Abstract Coulomb interactions among electrons and holes in 2D semimetals with overlapping valence and conduction bands can give rise to a correlated insulating ground state via exciton formation and condensation. One candidate material in which such excitonic state uniquely combines with non‐trivial band topology are atomic monolayers of tungsten ditelluride (WTe 2 ), in which a 2D topological excitonic insulator (2D TEI) forms. However, the detailed mechanism of the 2D bulk gap formation in WTe 2 , in particular with regard to the role of Coulomb interactions, has remained a subject of ongoing debate. Here, it shows that WTe 2 is susceptible to a gate‐tunable quantum phase transition, evident from an abrupt collapse of its 2D bulk energy gap upon ambipolar field‐effect doping. Such gate tunability of a 2D TEI, into either n ‐ and p ‐type semimetals, promises novel handles of control over non‐trivial 2D superconductivity with excitonic pairing.